1. Field of the Invention
The present invention is related to a method of performing device-to-device communication between two user equipment, and more particularly, to a method of performing device-to-device communication between two user equipment by monitoring synchronization signals using carrier sensing technology.
2. Description of the Prior Art
In a wireless communication system, two devices may communicate with each other via a base station, or directly using device-to-device (D2D) technology. The D2D technology may adopt two modes for resource allocation: network mode or client mode.
When two devices in coverage of abase station intend to perform D2D communication in the network mode, the base station is configured to allocate necessary resources to the two devices. However, if the base station is overloaded or has insufficient resources, transmission delay may influence the efficiency of D2D communication. Also, it is not possible to perform. D2D communication in the network mode when the two devices are out of coverage of the base station.
When two devices intend to perform D2D communication in the client mode, a specific resource is selected from a resource pool. Uncensored by any base station, a media access control method is required in order to avoid data collision when the two devices contend for D2D resources. Such media access control method may include, but not limited to, a carrier sense multiple access/collision detection (CSMA/CD) scheme or a carrier sense multiple access/collision avoidance (CSMA/CA) scheme. In a prior art D2D communication method, a device performs carrier sensing by monitoring data transmitted by other devices on the network, thereby lowering the chance of data collision. However, for the periodic transmission of D2D voice communications, carrier sensing is not an efficient way of resource allocation. Also, hidden node problem exists when an ad-hoc wireless communication system performs D2D communication in the client mode. Hidden node problem may cause data collision when a first device and a second device, both located out of the communication range of each other, intend to send data to a third device at the same time. Therefore, there is a need for a method of resource allocation in order to perform D2D communication with low transmission delay, high spectrum usage and high network coverage.